It is common knowledge that the operations that are necessary to carry out a printed circuit board involve an insolation step, especially for the photoetching definition of strip conductors. The corresponding installation is used to expose to ultraviolet rays, during a given time, the printed circuits covered with a film or a photosensitive resist through an artwork to insolate the corresponding part of the resist or of the photosensitive film defined by this artwork.
It is naturally understood that in this operation a fundamental point consists in obtaining a precise positioning of the artwork with respect to the printed circuit on which insolation is to be made.
The great majority of this type of machines only allows for the ultraviolet exposure of one side of the printed circuit plate. However, when the printed circuit plate is of the double-sided type, which is more and more frequent, the use of such machines is not very adapted as it requires the plate to pass twice inside the exposure machine which then requires two positioning operations of the artwork on its support with respect to the printed circuit.
To overcome this drawback, some insolation machines have already been proposed which allow a simultaneous insolation through artworks of both sides of the printed circuit. Such machines are described in particular in U.S. Pat. No. 5,337,151 and in European patent application EP 618 505.
The machine described in the above-mentioned U.S. patent, is based on the principle that consists in positioning with a mechanical centring the lower support and the upper support of artwork and in moving the artwork by means of a pair of fingers that are coupled with one another with respect to the unit made up of the lower and upper supports of artworks.
This machine has numerous drawbacks, owing particularly to the fact that the upper artwork is not positioned accurately with respect to the lower artwork and to the fact that the printed circuit cannot be precisely moved as required by means of two coupled fingers because of the risk of deflection of the fingers for moving the printed circuit.
Furthermore, this machine does not allow for the separate positioning of the upper artwork with respect to the upper side of the printed circuit and the positioning of the lower artwork with respect to the lower side of the printed circuit. Yet such a possibility can be useful in certain situations.
Concerning the European patent also mentioned above, said patent corresponds to an efficient machine insofar as the printed circuit moves with respect to the lower and upper artworks by means of two independent fingers which allow for a right positioning of the printed circuit. Also, in the machine described in this patent, there is a real positioning of the upper artwork with respect to the lower artwork. However, this machine does not allow for a separate positioning of the upper artwork with respect to the upper side of the printed circuit and a positioning of the lower artwork with respect to the lower side of the printed circuit. Further, this machine also presents risks of positioning errors because of the deflection of the fingers used for positioning the printed circuit.
To overcome these drawbacks, it is an object of the present invention to provide an installation of light exposure for a double-sided printed circuit allowing the eviction of the above-mentioned drawbacks and especially, when necessary, to achieve a separate positioning with respect to the printed circuit of the upper support of the artwork and of the lower support of the artwork.